KR20210059335A - Liquefied gas storage tank and ship having the same - Google Patents

Abstract

The present invention relates to a liquefied gas storage tank and a ship. The liquefied gas storage tank of the present invention is the liquefied gas storage tank comprising a weld used for welding of a Ni alloy steel base material, wherein the weld includes 0.025 to 0.2 wt% of carbon (C); 0.2 to 1 wt% of silicon (Si); 7 wt% or less of manganese (Mn); 10 to 20 wt% of nickel (Ni); 15 to 20 wt% of chromium (Cr); 2 to 5 wt% of molybdenum (Mo); and 0.05 to 0.17 wt% of nitrogen (N).

Description

Liquefied gas storage tank and ship {LIQUEFIED GAS STORAGE TANK AND SHIP HAVING THE SAME}

The present invention relates to a liquefied gas storage tank and a ship.

With continuous industrialization and technological development, the use of storage refrigerants from -80℃ to -196℃ is increasing, and accordingly, 2~9% Ni alloy steel, Invar, austenitic stainless steel, Al, etc. are applied as base materials.

In particular, a 9% Ni steel base material is used for the LNG fuel tank. At the current level, welds containing more than 60% Ni are used, and'Inconel 718' or'Inconel 625' is mainly used. Such a material has excellent high strength and cryogenic toughness, but has very high sensitivity to high temperature cracking, and is an expensive material due to its high Ni content, and has been limitedly used in the industry.

Such a material has excellent high strength and cryogenic toughness, but has a very high sensitivity to high temperature cracking, and is an expensive material according to a high Ni content, and has a problem of limited use in the industry.

In addition, since most of these conventional Ni-based weldments are constructed by SMAW (Shielded Metal Arc Welding), there is a problem that production efficiency is extremely low and high efficiency of the welding construction is required.

In addition, although high manganese steel was developed as a new material as a cryogenic steel, there is a problem that it is somewhat difficult to apply to the industrial world because it has excellent high strength and cryogenic toughness due to the great occurrence of fumes and spatters, but its weldability is very poor.

Accordingly, there is a need for research and development on a Ni-based weldment that has excellent economic efficiency by reducing the Ni content and has excellent high strength, high toughness, high temperature crack susceptibility, and weldability.

The present invention was created to solve the problems of the prior art as described above, and an object of the present invention is to reduce the Ni content in the weldment used for the welding of the Ni alloy steel base material, while having excellent economic efficiency, high strength, high toughness, high temperature crack susceptibility. And it is to provide a liquefied gas storage tank and ship in which the alloy composition of the Ni-based weldment is optimized so as to have excellent weldability.

In the liquefied gas storage tank according to an aspect of the present invention, in a liquefied gas storage tank including a weldment used for welding of a 2-9% Ni alloy steel base material, the weldment is, in weight%, carbon (C): 0.025 ~0.2%, Silicon (Si): 0.2~1%, Manganese (Mn): 7% or less, Nickel (Ni): 10~20%, Chromium (Cr): 15~20%, Molybdenum (Mo): 2~ It is characterized in that it contains 5%, nitrogen (N): 0.05 to 0.17%.

Specifically, the weldment may further contain tungsten (W): 1% or less.

Specifically, the weldment may further contain niobium (Nb): 1% or less.

Specifically, the weldment may further contain copper (Cu): 1% or less.

Specifically, the weldment may further include titanium (Ti): 1% or less.

Specifically, the weldment may satisfy a relational expression of 0.12 ≤ C + N ≤ 0.33.

Specifically, the weldment has an austenite single-phase structure, and _{may satisfy the relations 17≤Cr eq} ≤24, 18≤Ni _eq ≤28, wherein, Cr _eq (Cr equivalent) = Cr+ Mo+1.5Si +0.5Nb, and Nieq (Ni equivalent) = Ni + 30C + 0.5Mn + 25N.

A ship according to another aspect of the present invention is characterized in that the liquefied gas storage tank described above is mounted.

The liquefied gas storage tank and ship according to the present invention have excellent physical properties and excellent workability by optimizing the alloy composition of the welded material used for welding the base material of 2 to 9% Ni alloy steel, and full-fledged welding is possible. It has the effect of minimizing the occurrence of cracks while showing good weldability.

In addition, it is possible to secure price competitiveness in liquefied gas storage tanks and ships due to excellent economical efficiency through reduction of the Ni content of the weldment.

1 is a schematic side view of a ship having a liquefied gas storage tank according to an embodiment of the present invention.
2 is a table summarizing the chemical composition ratio for a weldment according to an embodiment of the present invention.
3 is an experiment table for a weldment according to an embodiment of the present invention.
4 is a graph showing the relationship between tensile strength and impact toughness according to C and N contents of a weldment according to an embodiment of the present invention.
5 is a Schaeffler-diagram of a predicted phase of a weldment according to an embodiment of the present invention.

Objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments in conjunction with the accompanying drawings. In adding reference numerals to elements of each drawing in the present specification, it should be noted that, even though they are indicated on different drawings, only the same elements are to have the same number as possible. In addition, in describing the present invention, when it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic side view of a ship having a liquefied gas storage tank according to an embodiment of the present invention.

Referring to FIG. 1, a ship 1 according to an embodiment of the present invention includes a liquefied gas storage tank CT, an engine room ER in which an engine system ES is located, and an engine room ER. ) It may include an engine casing (EC), a stack (F) and a deck house (DH) located on the top.

A plurality of liquefied gas storage tanks CT may be provided, and may be arranged side by side inside the hull. The liquefied gas storage tank CT of this embodiment may be arranged in a row along the longitudinal direction of the hull. However, the number, size, and shape of the liquefied gas storage tank CT may be variously modified.

For example, in the case of a container carrier other than a liquefied gas carrier, the liquefied gas storage tank CT may be formed in the form of a pressure vessel (Type C), and one or more may be provided on the deck.

The liquefied gas may be LPG, LNG, ethane, or the like, and may mean liquefied natural gas (LNG) as an example. In addition, the liquefied gas may be used as a term encompassing all of a liquid state or a gaseous state that has been naturally vaporized or forced to vaporize.

An engine room (ER) in which the engine system (ES) is placed is provided at the stern side of the ship (1), and the engine system (ES) placed in the engine room (ER) is an engine that provides the propulsion power of the ship (1). Poem). Although not specifically shown, the engine is connected to the propeller through a shaft, and consumes fuel to generate rotational force to rotate the propeller, so that the wake generated by the rotation of the propeller can advance the ship 1 .

The engine casing EC is provided above the engine room ER. The engine casing EC may have an exhaust pipe (not shown) that transmits exhaust generated from the engine system ES to the stack F.

The stack F is provided above the engine casing EC, and discharges exhaust to the outside.

The deck house (DH) is located on the upper part of the hull, and various living facilities for the crew's onboard residence and various navigational facilities for the voyage of the ship (1) are arranged. The deck house (DH) may consist of a plurality of floors, and may include a cabin, a control room, and other convenience facilities in which crew members can reside.

The ship (1) of the present invention is a gas carrier (LPGC, LNGC, etc.) equipped with a liquefied gas storage tank (CT) as a cargo tank on board, or a liquefied gas storage tank on board/offboard to use liquefied gas as fuel. It can cover ships on board, and furthermore, it can cover all offshore structures with liquefied gas storage tanks in addition to general commercial ships that transport cargo.

2 is a table summarizing the chemical composition ratio for a weldment according to an embodiment of the present invention, FIG. 3 is an experimental table for a weldment according to an embodiment of the present invention, and FIG. 4 is a table according to an embodiment of the present invention. It is a graph showing the relationship between the tensile strength and impact toughness according to the C and N contents of the weldment, and FIG. 5 is a Schaeffler-diagram of the phase prediction of the weldment according to an embodiment of the present invention.

A weldment according to an embodiment of the present invention is a weldment used for welding of a 2 to 9% Ni alloy steel base material, and includes a flux cored wire, a flux or a welding bead constituting the flux cored wire. Alternatively, it may include a submerged arc wire, a core constituting the submerged arc wire, or a welding bead.

A weldment according to an embodiment of the present invention relates to a weldment used when welding 2 to 9% Ni alloy steel.

In general, 2~9% Ni alloy steel-only weldments use a Ni core and a Mo shell. Weldments using Ni core and Mo shell are too expensive to be widely applied to the entire industry due to the high cost of the product itself as a large amount of expensive alloys such as Ni, Mo, and W are added.

Accordingly, the present invention can provide a weldment having excellent physical properties and weldability while applying the alloy content of an expensive material to a minimum compared to the prior art.

Hereinafter, in the liquefied gas storage tank (CT) including the welding portion of the 2 ~ 9% Ni alloy steel base material according to an embodiment of the present invention, in detail with respect to the weld used when welding the welding portion of the 2 ~ 9% Ni alloy steel alloy steel Explain.

In one embodiment of the present invention, flux-cored arc welding (FCAW, Flux Cored Arc Welding) was performed on the weldment, and welding was performed with a heat input of 13 kJ/cm in a condition _{of 100% CO 2 on a 9Ni steel base material, and a wire diameter} Was used 1.2mm.

As shown in FIG. 2, as shown in FIG. 2, the welded metal component obtained by welding is% by weight, C: 0.025 to 0.2%, Si: 0.2 to 1%, Mn: 7% or less, Ni: 10 to 20%, Cr: 15-20%, Mo: 2-5%, N: 0.05-0.17%.

In addition, the welded product may further include a welded metal component obtained by welding in wt%, W: 1% or less, Nb: 1% or less, Cu: 1% or less, or Ti: 1% or less. The numerical values of each of these welded metal components can be obtained through an experimental table (refer to FIG. 3) for a weldment.

In addition, the weldment can optimize the tensile strength and impact toughness according to the C and N content of the weldment, and satisfies the relation 0.12 ≤ C + N ≤ 0.33. This can be seen through the experimental table of FIG. 3 and a graph showing the relationship between the tensile strength and impact toughness according to the C and N contents of the weldment of FIG. 4.

Also, a weldment, the austenite (Austenite) has a single-phase tissue, satisfies 17≤Cr _eq ≤24, 18≤Ni _eq ≤28 relationship.

In the above, Cr _eq (Cr equivalent) = Cr+ Mo+1.5Si+0.5Nb, and Ni _eq (Ni equivalent) = Ni + 30C+ 0.5Mn + 25N.

This can be seen from the experimental table of FIG. 3 and the phase predicted Separ diagram of the weldment of FIG. 5 (Schaeffler-diagram).

The yield strength of the weld joint using the weldment obtained by the above composition ratio is 400 MPa or more, the tensile strength is 600 MPa or more, the elongation is 25% or more, and the impact toughness can satisfy 27J or more at -196°C.

As described above, the weldment of the present invention uses an austenitic stainless steel having excellent cryogenic toughness and weldability, and can have excellent economy by replacing the existing Ni content of 60% or more with a Ni level of 20% or less, and high temperature. It can have excellent weldability by greatly improving the crack susceptibility.

In addition, austenitic stainless steel generally has excellent cryogenic toughness, but its strength is less than 150 MPa compared to 2~9Ni steel, making it difficult to apply. And excellent weldability can be obtained.

Description of each component constituting the weldment of the present invention is as follows.

C: 0.025~0.2%

Carbon (C) is a strong austenite stabilizing element, and is a component that serves to improve strength and hardness. If the C content is less than 0.025%, austenite stabilization is unstable, and it cannot be said that the effect of improving the strength is sufficiently obtained. On the other hand, when it exceeds 0.2%, high temperature cracking resistance and toughness are deteriorated, and there is a problem that the occurrence of spatter increases.

Therefore, in this embodiment, it is preferable to limit the content of C to 0.025 to 0.2%.

In this embodiment, the C source of the deposited metal may be C reduced from metal carbides such as Mn-C, Cr-C, and WC contained in wires and fluxes, CO _{2 gas in the shield gas, and slag components.}

Si: 0.2~1%

Silicon (Si) is a component that improves deoxidation and weldability, and if its content is less than 0.2%, there is a problem that the deoxidation power is insufficient and the bead spreadability is deteriorated. On the other hand, if the content exceeds 1%, the weld is segregated. There is a problem that lowers the low-temperature impact toughness by causing a problem and adversely affects the weld crack susceptibility.

Therefore, in this embodiment, it is preferable to limit the content of Si to 0.2 to 1%.

In this embodiment, the Si source of the deposited metal may be Si reduced from a slag component such as Si and Fe-Si alloys, or SiO, etc., contained in wires and fluxes.

Mn: 7% or less

Manganese (Mn) is an austenite stabilizing element, and is a component that improves the flowability of slag to improve the bead shape and maintains the proper strength and toughness of the weld. In order to obtain the above-described effect, if it exceeds 7%, it may cause a rapid decrease in toughness, and since a large amount of welding fumes is generated, the weldability is deteriorated, which is not preferable.

Therefore, in this embodiment, it is preferable to limit the content of Mn to 7% or less.

On the other hand, in this embodiment, the Mn source of the deposited metal may be metal Mn, Fe-Mn alloy, MnO ₂ and MnCO ₃ included in the wire and flux, and the amount of Mn of the deposited metal can be adjusted by the addition of any. have

Ni: 10-20%

Nickel (Ni) is an austenite stabilizing element, and is a component that plays a role in maintaining the proper strength and toughness of the weld. In order to obtain the above-described effect, it is necessary to contain Ni in an amount of 10% or more. However, when the content exceeds 20%, the strength decreases, which is not preferable.

Therefore, in this embodiment, it is preferable to limit the content of Ni to 10 to 20%.

On the other hand, the Ni source of the deposited metal in this embodiment may be a metal Ni, an Fe-Ni alloy, etc. included in the wire and the flux, and the amount of Ni of the deposited metal can be adjusted by adding any of them.

Cr: 15-20%

Although chromium (Cr) is a ferrite stabilizing element, it has the effect of improving the strength of the weld metal. If it is less than 15%, there is no effect, and if it exceeds 20%, chromium carbide is excessively formed, thereby reducing toughness.

Therefore, in this embodiment, it is preferable to limit the content of Cr to 15 to 20%.

On the other hand, the Cr source in the deposited metal of this embodiment may be metal Cr, Fe-Cr alloy, Cr2O3, etc. contained in the wire and flux, and the amount of Cr in the deposited metal can be adjusted by adding any of them.

Mo: 2~5%

Molybdenum (Mo) has the effect of improving the strength and impact toughness of the deposited metal. If the Mo content is less than 2%, it is difficult to expect the above-described effect, whereas if it exceeds 5%, the toughness of the deposited metal is lowered.

Therefore, in this embodiment, it is preferable to limit the content of Mo to 2 to 5%.

On the other hand, the Mo source in the deposited metal of the present embodiment may be a metal Mo and an Fe-Mo alloy contained in wires and fluxes, and the amount of Mo of the deposited metal can be adjusted by adding any of them.

N: 0.05~0.17%

Nitrogen (N) is a strong austenite stabilizing element, and has an effect of improving the strength of the deposited metal due to the solid solution effect. In addition, the reduction rate of impact toughness is less than that of other reinforcing elements, so it is widely applied as a reinforcing element to stainless alloy systems.

If the nitrogen content is less than 0.05%, it is difficult to expect the above-described effect, whereas if it exceeds 0.17%, defects such as pores are generated in the deposited metal, and the toughness of the deposited metal is deteriorated.

Therefore, in this embodiment, it is preferable to limit the content of N to 0.05 to 0.17%.

W: 1% or less

Tungsten (W) has an effect of improving the strength of the deposited metal. Such W reacts with the carbon of the weld, so that an effect of improving strength can be expected, but it causes a decrease in impact toughness.

Therefore, in the present invention, it is preferable to limit the content of W to 1% or less.

On the other hand, the W source in the deposited metal of this embodiment may be TiO ₂ oxide, Fe-Nb, Fe-W, Fe-V alloy, etc. contained in wires and fluxes.

Nb: 1% or less

Niobium (Nb) has an effect of improving the strength of the deposited metal. Such Nb reacts with the carbon of the weld and can be expected to improve strength, but it causes a decrease in impact toughness and high temperature cracking resistance.

Therefore, in the present invention, it is preferable to limit the content of Nb to 1% or less.

On the other hand, as the Nb source in the deposited metal of the present embodiment, TiO ₂ oxide, Fe-Nb, Fe-W, Fe-V alloy, etc. included in wires and fluxes may be used.

Cu: 1% or less

Copper (Cu) is an austenite stabilizing element, and serves to maintain the proper strength and toughness of the weld. In case of excessive addition, corrosion resistance and hot workability are deteriorated.

Therefore, in this embodiment, it is preferable to limit the content of Cu to 1% or less.

Ti: 1% or less

Titanium (Ti) generates carbides or nitrides in the weld, and can act as a nucleation site when solidified at high temperatures. In addition, it serves to increase the strength of the weld by making the austenite grains smaller.

Therefore, in this embodiment, it is preferable to limit the content of Ti to 1%.

In addition to the above-described components, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a typical manufacturing process, this cannot be excluded. Since these impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.

As described above, in this embodiment, by optimizing the alloy composition of the weldment used for the welding of the 2~9% Ni alloy steel base material, the physical properties are excellent and the full-scale welding is possible, so that the workability is excellent, and the cracking while showing good weldability There is an effect that can minimize the occurrence.

In addition, it is possible to secure price competitiveness in liquefied gas storage tanks and ships due to excellent economical efficiency through reduction of the Ni content of the weldment.

In the above, the present invention has been described based on the embodiments of the present invention, but this is only an example and does not limit the present invention, and those of ordinary skill in the field to which the present invention pertains will not depart from the essential technical content of the present embodiment. It will be appreciated that various combinations or modifications and applications not illustrated in the embodiments are possible in the range. Accordingly, technical contents related to modifications and applications that can be easily derived from the embodiments of the present invention should be interpreted as being included in the present invention.

1: Ship CT: Liquefied gas storage tank
ES: Engine system ER: Engine room
EC: Engine casing F: Stack
DH: Deck House

Claims (8)

In the liquefied gas storage tank containing a weldment used for welding of a Ni alloy steel base material,
The weldment,
By weight%, carbon (C): 0.025 to 0.2%, silicon (Si): 0.2 to 1%, manganese (Mn): 7% or less, nickel (Ni): 10 to 20%, chromium (Cr): 15 to A liquefied gas storage tank comprising 20%, molybdenum (Mo): 2 to 5%, nitrogen (N): 0.05 to 0.17%. The method of claim 1,
The welded material is tungsten (W): liquefied gas storage tank, characterized in that it further comprises 1% or less. The method of claim 1,
The welded material is a liquefied gas storage tank, characterized in that it further contains niobium (Nb): 1% or less. The method of claim 1,
The welded product is a liquefied gas storage tank, characterized in that it further contains copper (Cu): 1% or less. The method of claim 1,
The welded material is titanium (Ti): Liquefied gas storage tank, characterized in that it further comprises 1% or less. The method of claim 1,
The liquefied gas storage tank, characterized in that the weldment satisfies a relational expression of 0.12 ≤ C + N ≤ 0.33. The method of claim 1,
The weldment is austenite (Austenite) has a single-phase tissue, 17≤Cr _eq ≤24, a liquefied gas storage tank which satisfy the following relational expression 18≤Ni _eq ≤28.
Above,
Cr _eq (Cr equivalent) = Cr+ Mo+1.5Si+0.5Nb,
Ni _eq (Ni equivalent) = Ni + 30C+ 0.5Mn + 25N. A ship, characterized in that the liquefied gas storage tank according to any one of claims 1 to 7 is mounted.

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